Patients with neurofibromatosis type 1 (NF1) develop benign tumors of peripheral nerve known as neurofibromas and malignant peripheral nerve sheath tumors (MPNSTs), a highly aggressive form of Schwann cell neoplasm that arises from neurofibromas. Inappropriate stimulation by growth factors is thought to cooperate with mutations of tumor suppressor genes such as NF1 and p53 to promote MPNST tumorigenesis. We hypothesized that proteins from the neuregulin-1 (NRG-1) family of growth and differentiation factors are among the molecules promoting the proliferation and/or survival of neoplastic Schwann cells in MPNSTs. To test this hypothesis, we generated transgenic mice expressing the NRG-1 isoform glial growth factor-23 (GGF23) in Schwann cells (P0-GGF23 mice) and found that these animals develop multiple neurofibromas and MPNSTs. We have also found that human neurofibromas and MPNSTs coexpress multiple NRG-1 isoforms and their erbB receptors and that the proliferation of human MPNST cell lines is profoundly inhibited by treatment with the small molecular erbB inhibitors PD158780 and PD168393. Based on these preliminary studies, we hypothesize that constitutive activation of erbB receptors is essential for the proliferation and/or survival of human MPNST cells and that decreasing erbB activity with PD168393 and/or 4D5, the anti-erbB2 antibody from which Herceptin was derived, will retard the proliferation and survival of these cells. We will partner human MPNST cell lines, mouse lines derived from MPNSTs arising in P0-GGF23 mice and the P0- GGF23 mouse model to critically test the hypotheses that: 1) inhibition of the NRG-1 receptors (erbB2, erbB3 and/or erbB4) decreases the proliferation and/or survival of MPNST cells in vivo and 2) NRG-1 promotes the proliferation and/or survival of MPNST cells by activating specific neurofibromin-regulated Ras proteins and their downstream effectors. These studies will critically evaluate novel therapies for MPNSTs that utilize effective, existing erbB inhibitors and will establish a strong basis for the future development of even more effective therapies precisely targeting critical NRG-1 regulated cytoplasmic signaling molecules, alone or in combination with erbB inhibitors, in NF1-associated MPNSTs. Patients with neurofibromatosis type 1 (NF1) develop benign tumors of peripheral nerve known as neurofibromas, and malignant peripheral nerve sheath tumors (MPNSTs), a highly aggressive form of Schwann cell neoplasm that arises from neurofibromas. Inappropriate stimulation by growth factors is thought to cooperate with mutations of tumor suppressor genes such as NF1 and p53 to promote MPNST tumorigenesis.